Integrated circuits are made possible by processes which produce intricately patterned material layers on substrate surfaces. Producing patterned material on a substrate requires controlled methods for removal of exposed material. Chemical etching is used for a variety of purposes including transferring a pattern in photoresist into underlying layers, thinning layers or thinning lateral dimensions of features already present on the surface. Often it is desirable to have an etch process which etches one material faster than another helping e.g. a pattern transfer process proceed. Such an etch process is said to be selective to the first material. As a result of the diversity of materials, circuits and processes, etch processes have been developed with a selectivity towards a variety of materials.
A Siconi™ etch is a remote plasma assisted dry etch process which involves the simultaneous exposure of a substrate to H2, NF3 and NH3 plasma by-products. Remote plasma excitation of the hydrogen and fluorine species allows plasma-damage-free substrate processing. The Siconi™ etch is largely conformal and selective towards silicon oxide layers but does not readily etch silicon regardless of whether the silicon is amorphous, crystalline or polycrystalline. The selectivity provides advantages for applications such as shallow trench isolation (STI) and inter-layer dielectric (ILD) recess formation.
FIGS. 1-2 show a flowchart of dry etch processing steps and associated schematic side-views of silicon oxide trimmed from trenches on a patterned substrate. The process begins when a patterned substrate is transferred into the processing region (operation 110). The silicon oxide selective dry etch begins (operation 120) when plasma by-products are delivered to the processing region. The selective dry etch results in the consumption of silicon oxide 150-1 from within the trenches and the associated production of solid residue 155 above the remaining silicon oxide 150-2.
The Siconi™ process produces solid by-products 155 which grow on the surface of the substrate as substrate material is removed. The solid by-products are subsequently removed via sublimation (operation 130) when the temperature of the substrate is raised. Silicon oxide surface roughness and inter-trench etch rate variability may be observed following sublimation.
Methods are needed to provide greater uniformity of dry etch processes.